During the past year we have investigated an intra-diol cleaving dioxygenase enzyme. This work has led to a detailed mechanism of action for these types of enzymes. In January, 1978, we will start a systematic Mossbauer and EPR study on extra-diol cleaving dioxygenases. Three different enzymes have been purified for this study. Biochemical and physical studies indicate that the active sites of these enzymes are made up of as yet unrecognized metal complexes, possibly spin-coupled structures. The most promising enzyme of this class seems to be 4,5 protocatechuate dioxygenase from P. testosteronii, for which our co-workers (J. D. Lipscomb's group) have developed an efficient purification procedure. In addition, we will continue our work on 3,4 protocatechuate dioxygenase, desulphoredoxin, and the cytochromes c' and c2.